Titration calculations:?

Question

Hi im having difficulty remember what i have to do in order to work out the concentration of the acid and the sodium carbonate,

so far ive got:

Na2C03 = 106 g (RMM)
The amount of sodium is 2.65 g being used in distilled water to fill 250 cm^3 solution


and Na2SO4 = 142 g (RMM)
There is a total of 250 cm^3 solution for the acid.


where do i begin to even do this? i know that i need c = N0 of moles / volume.

Answer 1

I don't quite understand what you're trying to do here..from the way you've written the question it makes it sound like you're trying to titrate the two, but sodium sulphate is a neutral salt, not an acid. Do you mean Na2CO3 + H2SO4 -----> Na2SO4 + H2O + CO2?

I'm going to assume so..
In which case the concentration of the base is worked out by:
Concentration = No. of moles/volume
No. of moles = mass/RMM
So no. of moles of Na2CO3 = 2.65/106 = 0.025
(note 0.25l not 250ml as we want to find the molar concentration ie. the no. of moles per litre)

So concentration = 0.025/0.25 = 0.1M/l

Now, to find the concentration of the sodium sulphate; from the equation I wrote earlier you can see that they react in a 1:1 ratio; each molecule of Na2CO3 produces one molecule of Na2SO4. So, 0.025 moles of Na2CO3 will produce 0.025 moles of Na2SO4. As the volume of solution you are using is exactly the same as it was before, the molar concentration will also be the same; 0.1M

Answer 2

yes conc= amount/volume.
The amount in moles = mass (g) / RMM (g/mol)
You can then use this to calculate the amount and concentration.

I think you are missing some information though when you say the amount of sodium is 2.65g is that sodium metal, sodium carbonate or sodium sulphate? Also which acid? It sounds like maybe you were doing a titration between Na2CO3 and sulphuric acid H2SO4.

Na2CO3 + H2SO4 -----> Na2SO4 + H2O + CO2

the number of moles of sodium carbonate would equal the number of moles of sulphuric acid. So now you have worked out the amount of sodium carbonate you know the amount of sulphuric acid. The sulphuric acid volume is 250cm3 so now you can work out the concentration.

If that is not the titration you are trying to calculate, basically follow these steps to work yours out:

Write out the chemical equation, what is the ratio between the two reactants?

Usually you have either the volume and concentration, or a mass in grams for one reactant. Work out the amount in moles. Using either:
moles = conc x vol or moles = mass/ RMM

Multiply that number by the ratio of the reactants to give the number of moles of the other reactant e.g 1 mole of Na2CO3 = 1 mole of H2SO4.

Then calculate the concentration of your second reactant using conc = moles/ volume.


Always remember to convert volumes into dm3 (cm3/1000).